Refractory lining for rotary kilns



Sept. 8, 1959 R. P. HEUER REFRACTORY LINING FOR ROTARY KILNS 4 Sheets-Sheet l Filed Feb. l6, 1956 ///h/U U III s a .ll. a

' TTORNEY Sept. 8, 1959 R. P. HEUER REFRACTORY LINING FOR ROTARY KILNS Filed Feb. 16, 1956 4 Sheets-Sheet IS INVENTOR Sept. 8, 1959 R. P. HEUER REF'RACTORY LINING FOR ROTARY KILNS Filed Feb. 16, 1956 4 Sheets-Sheet 4 cral` Refra'c'toris Company, a` corporation of Pemsylvania Application-February 1 6 1956, SeriaPNb: 565332 7 Clams. (Cl-.-263--33) The present' inv'e'nton relates' to r'efractory linings for r'o'tary' klns used' for example in' the burning orcal'- ci'ni'ng of dbl'omit'e, magnesit'e, and other c'ompounds' o' f magnesia, Portland cement; other cement containing' calcium oxide, lime, and minerals and ores which' are compatible With a basic refractory lining.

A purpose of the invention is to mprove the service of basic refractories used in rotary klns by improvng the resistance of the basic refractory brick to mechanical failure on account of cracking' o' spalling transverse to the radius of the'kiln. V

A further purpose is toj line a rota'ry kiln With a' basic refractory brick which is" unfired and suitable for" use without previous' klr firing, the brick' being provided with internal steel' plates Comoldd' with the brick and ther'etbre intimately as'sticiated with the' refractjory'.

States Patefit i ice A further prp'ose' is to partiti'on the individual brick by internal platesiwhose major axes are perpendicular to the -hot face" of' the brick, subdividin'g th'e'brick laterlly into two'or more'cells' and reacting with the refractory to form strengthening columns which reduce' the tendenc'y of the brick to crack or spall because of temperature changes; v

A further purposeis' t'o provide'iriterna'l plates which lie radially or perpendicular to`theax`is of' the klri and facilitatethe retenton of a coating of kilr' charge onthe surface of the brick an'd' thus prolong the life of" the brick.

A further purpose 'is to co'm'biiie the' internal plateswith external plat'es' extendingtr'ansver'se to the ht face'an'd desirably physically secured'directly to the internal plates.

A further purpose is to" comold a refractor'y material such'a's magne'sia or' Chromite atthe endadjoining the hot* face and a` refractoryinsulating material at the end adjoining the" cold face;

Further' purposes appear in the specfica'tion and in the claims;

In the' drawir'gs' I'have chosen to illustrate a few only V' 2303254; Patented Sept. 8, 1959 2 The brick of Figure 7 has not only internal plates and eitei nl plates on the circu'mfer'ential sides but' also has extrjnal plate on the radial sdes.

Fig're' 8 is a side' el'evation of Figu'r'e 7 looking at the ci'fcui'rifereitil s'ide.

Figr'e`9 is a' section on'the line9-9` of Figura 8.

Figu're 10 is a perspecti've of the spacer plate's employed in the" brick of Figures 7 to 9; omitting the refractory.

Ngrir l1` is a diag'farn'matic central vertical section sheh/'ing the mblding of the refractory brick of Figur'es 7" to` 9, the mld' being' in open position.

Figure 12 is a digrammatie fragmentry section transtie'fs'e't'o the axis and' oi'rittin g the outer shell, showing a ro tary kilii liiiing employing the refr'actory brick of Figurs 7 to l 1 inclusive.

Figr'e 13' is a'di'agr'animatic fragment'ary section trans- Verse" to the a`xis, omitting the outer shell, showing a rotary kilnlir'ihg employi'n'g" the brick of Fig'ures l to 5, atr''ating" with the brick of Fig''r'e 7' to 11` inclusive.

Fig'ire 14 is a front elevation looking" at the hot' face, shwig an arch brick according' to the invention, ernplyihg' external plates oii' both the circumferential and rdifl sid aswll a's internal plates. s

F'gr 1`5 is a side' elevation looking' atthe circumf'ere tial s'ide f thear'chbrick of Figre'` 14.

Figure 16 is a section on the line 16-16 of Figur 15.

Figiii'e' 17 ,i`s` a perspective showing' the spacer plates uefd'ih v ng the'brick of Figurs' 14 to 1'6. i

Figur 18' is" a` digrainniatc central' vertical section showing a mold in open' position for' molding the refractry'brik' of Figres' 14" to' 16.

Fig'i'e l'9' is a"viewsiinilar to Figure 18 showing an altjthte costrtition' of spacer plates forthe brick of Figur-"s 141616: V

itlre'"20` 'is `a`diag ramatic fragmentet-y section transverse* to theaxisf through a"ro'tary kln lihing employing the" brick of Figures 14 to` 19,' and oniitting the outer s'lre'll' Piguill is apr'adia'l side elevatidnof a modified form o'f' brick according to` the in ention, employing basic refracftry'at* the hot end andrefractory insulation in com'o ea relti'i at the cold end; i e "e 2 2 is` a sectidn on'the line 22-42 of Figure 21.

Figur`e`23 is" a'diagranriiatic fragmentary section transverse to the axis showing a rotary kiln lining using th refractory brickofFigures 21 andZZ andomtting the outr she'll.

Rdtry' kiliis of the character of rotary cement klns are lined`w'ith" refractory brick which protect the shell from* the heat in the kiln. When the kiln operates at low tenip'eratures, fire clay or high 'alumna brick are suitable, but for highest tenperatures and where the charge' is" high inlirne or magnesia, basic brick containinfg mrethan o percent magnesia are used to minimize thech mical attack' of'the charge on: the kiln liningand obta n` greater refractoriness. Such brick 'are usually rrrade frdm 'refrctory magnesia such as periclase or dead Figure 4 is a perspectiveshowing the opposed external and internal spacer plates used in the brick of Figures 1 to 3; and'omitting" the refractory' material for clarity. FigureS is a central vertical section-'through the mold inopen position showing the 'molding` of a brick according to `Fi'gu'e's 1 to 3. Figure' 6 *is a diagrammatic'fragmentary section transverse' to the axis' and"omitting the'outershell, showing a rotary kilnlining e'iploying the brick of Figures 1 to 5. Figure'7'is'a frontelevation of a modified form of key brick accord'ing'td the' invention looking at the hot face;

burned magnesite, -a-ndthey may' co nsi'st' substar'tially"eri-' tircly of such-'materials On the 'other hand, chromite may be incorp'orated provided there is -at least 30 per: cent'of rnag'neia by Weight so that the primary ingredie`n'ts will ordin'arily be' magnesia or' 'a miXture of' mag nsia and ch'romite. In addition olivine or other siliceos materials may be added'up' to arnaxi'n'iuhr' o'f alio 1635 pe'rent of silica-in the refractory.

The .brick will also ordinarily having -a-- bonding-sub stance present to the eXtent of 1 to 10 percent by weight of the'dfy refractorynixturel Such bonding substances will-'ordinarily be' magnesiu'ni chloride,` mag`ne's`ium sulfatepchrornc acid,- sulfuric' acid, kaoliril rn'etallic iron or the like. The 'bonded brickare unfired'ani used `un*- fired, the heat 'in the kiln' developing-` a `cerantic bond.

Such unfired brick usually exhibit a lower thermal conductivity than fired brick and cause less heat conduction through the lining.

- In a rotary kiln it is important that the lining fit prop erly against the metallic shell of the kiln. If the refractory lining is to loosen, or if the refractory brick shrink when heated to firing temperature during use, the lining will be damaged when the kiln is rotated because the weight of the refractory brick and of the charge will not be properly carried by the shell as the kiln turns, On the other hand, it is Very objectionable to fit'the brick too tightly to the shell, as the increase in size of the brick which occurs during heating may cause the development of excessive compressive forces on the brick which will cause cracking.

Great 'advantage has developed from the use of iron or steel spacer plates, usually about inch thick, in the radial joints between basic refractory brick in a rotary kiln lining. These plates oxidze at the hot face forming iron oxide which may combine with the magnesia present in the brick to form magnesioferrite. When the plates are :at the joints oxdation is commonly accompanied by an increase in Volume of the plates. This increase in Volume is helpful in keeping the lining tight but unfortu nately the `action is not uniforrn throughout the thckness of the lining because oxidation takes place at the hot face and the subsequent reaction is most intensive at the hot face, whereas reaction at the cold face is negligible.

I have discovered that the service ch'aracterstics of basic refractory linings for rotary kilns can be greatly improved by extending comolded internal plates through the brick transverse to the hot face.

The internal plates employed in the present invention exhibit a substantially different -behavior from the external plates. Whereas in the external plates the functioning is almost entirely concerned with the strengthening of the lining by bonding together one brick with its neighbor, the internal plates greatly change the functioning of the internal structure of the brick by subdividng the brick into cells and then strengthening the cells by forming magnesioferrite at their partition walls.

Unlike the magnesioferrite which commonly forms from the external plates, the magnesioferrite forming by reaction with the comolded refractory on the interior of the brick is produced without appreciable increase in Volume, and therefore does not disrupt the brick structure.

It is important in the present invention to use bonded basic refractory brick prepared without previous kiln firng, since of course the steel plates would not re main through a refractory brick kiln operation.

The internal plates should always be in a position perpendicular to the axis or radial of the rotary kiln lining as far as possible.

In making up the brick according to the present invention, I preferably use refractory magnesia such as periclase or dead burnedmagnesite which preferably contains more than 85 percent of magnesia. The following are typical analyses of suitable magnesias by weight:

Sea Water Dead Bumed Periclase Magnesite The magnesia may where desired be mixed with up to 70 percent of Chromite by weight. The Chromite may for example be Cuban, Philippine, Grecian, Rhodesian or Transvaal Chromite, as desired.

It is preferable to use mixtures of course and fine grains, a suitable example of a desirable grain size mixture for rotary kiln brick being as follows:

The brick are desirably bonded with sulfuric acid, for example 1 percent by weight, and kaoln, suitably 1 to 3 percent by weight. Iron powder may be added where desired to the extent of 5 percent by weight.

The brick shown in Figures 1 to '5 inclusive is a key brick having a hot end 20, a cold end 21, radial sides 22 and circumferential sides 23, as well known in the art.

As shown, the hot end may Conveniently be straight but the cold end is desirably curved to fit the interior of the metallic shell of the kiln.

Opposed steel plate assemblies 24 are used, as best seen in Figure 4.

The spacer plates here shown and those described elsewhere heren are desirably formcd of iron or steel sheet or plate, which may be plain carbon steel or alloy steel including stainless steel if desired. The plate thickness is usually about inch, although plate thickness may as desired be used in the range from about inch or thinner to about inch or thicker.

The plate assemblies desirably consist of an external plate 25 which is preferably formed to fit the entire circumferential side of the brick and internal plates 26 transverse to the external plate which are preferably united as by welding at 27 to the external plates. While it will be recognized that a single internal plate can be used extending radially, it is preferable to use two radial internal plates as shown, each consisting of halves or portions extending from the opposite sides almost to the center. It will be evident that the question of whether the internal plates extend from opposite sides toward the center or extend entirely from one side is immaterial except in the technique of molding.

The plates should in any case extend at least 80 percent of the length of the refractory portion of the brick, although they preferably will not be carried through the heatinsulation portion if any at the cold end.

In molding the brick, a mold is used as shown in Figure 5 consisting of a lower die 28 and an upper die 30 movable toward one another, preferably by moving the upper die downward. The mold has sides 31 and side extensions 32 which define an interior space 33 in which the brick is to be formed.

One of the plate assemblies 24 is placed on the bottom die with the external plate 25 resting thereon and the internal plate halves 26 extending upwardly. A basic refractory mixture 34 is placed in the mold on the plate assembly 24 and another plate assembly 24 is placed on the top of the refractory either by hand or preferably is secured to the upper die by a magnetic chuck or other means as well known. The upper plate assembly has the external plate 25 extending across the bottom of the upper die and the interior plate halves 26 extending downwardly, parallel to and in line with the plate halves on. the lower plate assembly.

When the mold halves move together under a suitable forming pressure, a brick is produced as shown in Figures 1 to 3 with the interior plates and exterior plates united to the refractory by comolding.

The pressure app lied in molding will in any case exceed 1000 p.s.i., preferably exceeding 5000 p.s.i., and most desirably being at least 7000 p.s.i. or more.

The molded brick are desirably cured in carbon dioxide gas, as well known in the art, and dried and placed n service.

In the form of brick shown in Figures 1 to 3 inclusive, no external plates are provided at the radial sides 22.

The form of Figures 7 to 11 inclusive uses one plate assembly 24 along with a plate assembly 24' which has in addition to the external plate portion 25' extending along the ciroumferential side, U-shaped arms 35 which initia-lly extend out from the plate portion 25' at an angle greater than a right angle, but which under the molding pressurc are forced out square, as shown in Fig ure 7 and cover substantally all of the radial side.

Themo lding technique is: carrid ou tasz already d-' scribed except that the I plate assemblyt 24 is: placed? in' the: bottom of the mold before& the:` refractory` 'ist: added.: The:externa1:plate portion- 25 prior. to the moldingoperation is desirably not quite'wide'enoughttos extends across themold; butthe' armSSS en-'gage the'moldsids, and, as previously'explained,iare forced out:toroccupy the fill-1- width' when moldin'g. is finished:

In many casess the userwil'lrpreferrtoformsa kiln lining using the'brick of Figures 1 to 3 without external plates in 'the radiail joints. The lining wil-lbe' asshown in Figure 6. The internalplates wherrtheated ILSC-'VCG- willoxidize, but the iron oxide formed near the hot end will produce magnesioferrite `and-' di i'hiseinto theadjoining refractory withoutappreciable:increase in' Volume. In this manner the objectionable features of diiferential contraction' and expan'sion which attend the use of external plates'in the radal' joints Will'b'e avoidd. The radal internal plates tend tored'ce' spallingj and cracking, and facilitate the' retention of'a` coa'tin'g of the kiln charge o-n the hot face of therbrick whieh givesxalonger life to the brick, but they do not cause erratic overall exnanson.

Where external plates in radialjoints are desired, the user has the option' of 'employing'- loose plates in the radialjoints; or of'using the:brick'37 ofI-Tigures 7 to `9;.as shownin Figure 12.-

Where the user desires to avoid the double? exterion plates at the radal joints, he may use brick 36 according to Figures 1 to 3 alternating with brick 37 of Figures 7 to 9, as in Figure 12.

The Construction of Figu'es 1 to 13 inclusive uses key brick, which are more mechanically stable than the arch brick now conventionally used in rotary kiln linings. If, however, the user prefers arch brick, it is advantageous to use internal plates running transverse to the hot face in such arch brick.

Figures 14 to 16 show such an arch brick having a hot face 38, a cold face 40, and circumferential sides 41 and radal sides 42.

In molding the brick an upper metallic plate assenbly 43 is used having a flat external plate 44 which substantially covers the radal side and having welded thereon and extending transverse to the axis radal internal wedge plate halves 45, of which two are shown equally spaced. An opposed plate assembly 46 is provided which has an external plate portion 47 which as initially formed covers almost the entire lower radal side, but is slightly narrower than the mold of Figure 18, as shown. The plate portion 47 is joined to U-shaped arms 48 of wedge shape and join the plate portion 47 at an angle initially greater than a right angle, scaling to the mold sides.

The internal plate portions 45 from the opposite plate assemblies are in line and in the molded brick extend almost to the center. In molding as shown in Figure 18 the plate assembly 46 is first placed on the bottom die with the plate portions 45 and 48 upstanding and the plate arm portions 48 scaling against the sides 31 of the mold. Basic refractory rnixture 34 is then inserted in the mold and the plate assembly 43 is placed on top with the plate portions 45 sticking down as already described.

In the molded brick the arms 48 are forced out in right angle relation to the portion 47 as seen in Figure 14.

If plates should not be desired on the circumferential sides 41, the structure can be molded as shown in Figure 19 by using two plate assemblies 43 as shown.

The arch brick when placed in the lining form a rotary kiln lining as illustrated in Figure 20 where the brick are positioned at 50.

In some cases it is desrable to have the rotary kiln brick provided With insulation material in comolded relation to the refractory material and located at the cold end. This is illustrated in Figur-es 21, 22 and 23. This brick has a hot end 51, a cold end 52, radal sides 53 and circumferential sides 54.

Whereithebricl isshown' as being a key'brick, it= may alsob'em'ade of'archrform.` It is a matter of: selection: among the:` possibilities' presented by. the' invention as to' whether the external'plates" are provided on the' radal:

faces or not In the forml shown, thebasic refractory 56: extends from the hot end to the comolded joint 55 and' has plate ass'emblies 2'4 which? go-as: far toward the cold end as the joint: 55.7 andi otherwise are: generally similar to those' shown' in Figure 4: Atthe cold end the heat insulation: material 57 is provided.`

Inthete'chnique of molding,` apartition maybe inserted in the mold in the plane ofthe' paper oflFigureS, at the position* of? the joint 55, and refractory' material inserted on one side of the'partition'zandzheat insulaton material on the othersde. andthenthe partition' carefully with-- drawn, after whichthe mo'lding proceeds as usual.

The insulating' material may be caloinedfire' clay or calcined .kaoln which is bo'nded zwitli' a suitable bond such as aboutlOpercentof calcinedmagnesia plus about 1 percent ofi magnesium 'chloride or magnesium sulfate.

In. view of my invention and:` dsclosure, .variations and modifications to meetindividualf whirn tor: particular need willxdoubtless become'ev'dent to others skilled in the art, to obtaii allloripartof the benefi'ts :of my invention with outcopyingthe' structure' shown and I; therefore, claim all such insofa'r as they. fall withinthe reasonable. spirit and scope of my claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A refractory lining for a rotary kiln having .a longitudinal axis, said lining being adapted to extend circumferentially around said longitudinal axis of the kiln thus to hold a charge and comprising a plurality of basic refractory brick each having a refractory body containing more than about 30% magnesiurn oxide and said brick being u-nfired and suitable for use in the unfired condition, said brick having side faces in the lining and being disposed side by side at said faces, and each said brick having a small end which constitutes the hot end and having a larger opposite end, the refractory in each said brick being comolded with an internal steel plate subdividing said body into cells, the plate having opposite side surfaces lying between said cells and between opposite side faces of the corresponding brick in the lining and having an end surface directed inward toward the axis of the kiln, and each said brick including a steel spacer plate on a side face thereof in the lining, said steel spacer plate separat ing the refractory in the corresponding brick from the adjacent brick, and said plates in operation of the kiln being susceptible to oxidation at the hot ends of the brick thus producing bonds between the refractory bodies of the brick at said spacer plates and spall-resistant and corrosion-resistant columns of magnesioferrite inside the refractory bodies of the brick in the vicinity of said internal plates.

2. A refractory lining in accordance with claim l, in which there are a plurality of comolded internal steel plates spaced from each other in the interior of the refractory body of each individual brick subdividing said body into cells, said plates having opposite side surfaces lying between said cells and between opposite side faces of the corresponding brick in the lining and having end surfaces directed inward toward the axis of the kiln.

3. A refractory lining in accordance with claim 1, in which the brick are key-shaped and said opposite surfaces of the internal plates extend longitudinally of the kiln.

4. A refractory lining in accordance with claim 1, in which the brick are arch shaped and said opposite surfaces of the internal plates lie in plane perpendicular to the axis of the kiln.

5. A refractory lining in accordance with claim 1, in which said side faces of the brick in the lining extend circumferentially and longitudinally of the lining and the refractory of the brick is separated by steel spacer plates between the longitudinally and circumferentially extending side faces, the spacer plates between the longitudinally extending side faces of the brick being comolded with the refractoy material' of individual brick in the lining and directly contacting the refractory material of corresponding longitudinally extending side faces of adjacent individual brick in the lining.

6. A refractory lining in accordance With claim 1, in which the brick are integral composites, each brick having in unfired condition at the hot end a refractory material containing more than about 30% magnesium oxide and having refractory insulation at the cold end united to the refractory material by comolding.

7. A refractory lin-ing for a rotary kiln having a longitudnal axis, said lining being adapted to extend circumferentially around said longitudinal axis of the kiln thus to hold a charge and comprising a plurality of basic refractory brick each having a refractory body containing more than about 30% magnesium oxide and said brick being unfired and suitable for use in the unfired condition, said brick having side faces in the lining and being disposed side by side at said faces, and each said brick having a small end which constitutes the hot end and having a larger opposite end, the refractory in each said brick being comolded with an internal steel plate subdividing said body into cells, the plate having opposite side surfaces lying between said cells and between opposite side faces of the corresponding brick in the lining and having an end surface directed inward toward the axis of the kln, and each said brick including a steel spacer plate on a side face thereof in the linng, said steel spacer plate separating the refractory in the corresponding brick from the adjacent brick and being integral with said internal steel plate, and said plates in operation of the kiln being susceptible to oxidation at the hot ends of the brick thus producing bonds between the refractory bodies of the brick at said spacer plates and spall-resistant and corrosion-resistant columns of magnesoferrite inside the refractory bodies of the brick in the vicinity of said internal plates.

References Cited in the file of this patent UNITED STATES PATENTS 1,378,71O Meyerhofer May 17, 1921 1,823,356 Frink Sept. 15, 1931 2,230,142 Longacre Jan. 28, 1941 2,652,793 Heuer et al. Sept. 22, 1953 FOREIGN PATENTS 696,311 Great Britain Aug. 26, 1953 OTHER REFERENCES Pages 387 and 388 of Modern Furnace Technology by Ether-ington, 1938, published in London by Charles Griin & Co., Ltd. 

1. A REFRACTORY LINING FOR A TROTARY KILN HAVING A LONGITUDINAL AXIS, SAID LINING BEING ADAPTED TO EXTEND CIRCUMFERENTIALLY AROUND SAID LONGITUDINAL AXIS OF THE KILN THUS TO HOLD A CHARGE AND COMPRISING A PLURALITY OF BASIC REFRACTORY BRICK EACH HAVING A REFRACTORY BODY CONTAINING MORE THAN ABOUT 60% MAGNESIUM OXIDE AND SAID BRICK BEING UNFIRED AND SUITABLE FOR USE IN THE UNFIRED CONDITION, SAID BRICK HAVING SIDE FACES IN THE LINING AND BEING DISPOSED SIDE BY SIDE AT SAID FACES, AND EACH SAID BRICK HAVING A SMALL END WHICH CONSTITUES THE HOT END AND HAVING A LARGE OPPOSITE END, THE REFRACTORY N EACH SAID BRICK BEING COMOLDED WITH AN INTERNAL STEEL PLATE SIBDIVIDING SAID BODY INTO CELLS, THE PLTE HAVING OPPOSITE SIDE SURFACES LYING BETWEEN SAID CELLS AND BETWEEN OPPOSITE SIDE FACES OF THE CORRESPONDING BRICK IN THE LINING AND HAVING AN END SURFACE DIRECTED INWARD TOWARD THE AXIS OF THE KILN AND EACH SIAD BRICK INCLUDING A STEEL SPACER PLATE ON A SIDE FACE THEREOF IN THE LINING, SAID STEEL SPACER PLATE SEPARATING THE REFRACTORY IN THE CORRESPONDING BRICK FROM THE ADJACENT BRICK, AND SAID PLATES IN OPERATION OF THE KILN BEING SUSCEPTIBLE TO OXIDATION AT THE HOT ENDS OF THE BRICK THUS PRODUCING BONDS BETWEEN THE REFRACTORY BODIES OF THE BRICK AT SAID SPACER PLATES AND SPALL-RESISTANT AND CORROSION-RESISTANT COLUMNS OF MAGNESIOFERITE INSIDE THE REFRACTORY BODIES OF THE BRICK IN THE VICINITY OF SAID INTERNAL PLATES. 